In recent years, a display device capable of screen input by bonding a touch panel to a display screen of the display device such as a liquid crystal display, a plasma display, or an organic EL display is widely used. This touch panel has a structure, in which glass plates or resin films having a transparent electrode formed thereon are bonded to one another with a slight gap, and if necessary, a transparent protective plate of glass or resin is bonded onto the touch surface.
There is a technique, in which a pressure sensitive adhesive double coated sheet is used to bond a glass plate or film having a transparent electrode formed thereon to a transparent protective plate of glass or resin in a touch panel, or to bond a touch panel to a display unit. However, there is a problem that air bubbles are easily generated when a pressure sensitive adhesive double coated sheet is used. A technique, in which a glass plate or film having a transparent electrode formed thereon is bonded to a transparent protective plate of glass or resin with an ultraviolet curable resin composition having flexibility, or a touch panel is bonded to a display unit with an ultraviolet curable resin composition having flexibility, has been suggested as an alternative technique to a pressure sensitive adhesive double coated sheet.
Meanwhile, a light shielding portion of belt shape is formed at the outermost edge of a transparent protective plate in order to improve the contrast of a display image. In a case in which the transparent protective plate having a light shielding portion formed thereon is bonded with an ultraviolet curable resin composition, insufficient ultraviolet rays reach the ultraviolet curable resin in the light shielded region, which corresponds to the shade of the light shielding portion, because of the light shielding portion, and thus the curing of the resin in the light shielded region is not sufficient. If the curing of resin is not sufficient, problems such as display unevenness in the display image near the light shielding portion occur.
As a technique to improve the curing of resin in a light shielded region, Patent Literature 1 discloses a technique, in which an organic peroxide is contained in an ultraviolet curable resin, and the resin thus obtained is irradiated with ultraviolet rays and then heated, whereby the resin in a light shielded region is cured. However, it is concerned that a heating process causes damage to a liquid crystal display device and the like. Moreover, there is a problem of poor productivity since the heating process requires generally 60 minutes or longer time to secure sufficient curing of resin. In addition, Patent Literature 2 discloses a technique, in which the resin in a light shielded region is cured by irradiating with ultraviolet rays from the outer side surface of the light shielding portion forming surface. However, there is limitation in this technique since it is sometimes difficult to irradiate the resin with ultraviolet rays from the side surface depending on the shape of a liquid crystal display device. In addition, Patent Literature 3 discloses a technique, in which slow acting property of a cationically polymerizable ultraviolet curable resin is used, but the resin after curing is poor in flexibility.